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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*! \example modbus/server
\title Modbus Server
\ingroup qtserialbus-examples
\examplecategory Connectivity
\brief The example implements a Modbus server application.
The example acts as Modbus server. It receives standard Modbus requests,
adjusts its internal states based on the request and responds with the
appropriate reply.
This example must be used in conjunction with the
\l {modbus/client}{Modbus Client example}.
This example should be started and put into the listen state before the
Modbus client example is started. Subsequent interactions between the two
examples use the Modbus protocol.
Key classes used in this example:
\list
\li \l QModbusServer
\li \l QModbusDataUnit
\endlist
\image ../images/modbusserver.png
{Modbus Server with connection settings, Coils and Discrete Inputs
checkboxes, Input Registers and Holding Registers columns}
\section1 Creating a QModbusServer
An instance of \l QModbusServer is required to perform any communication.
Depending on the specified connection type, the example can instantiate a
\l QModbusRtuSerialServer (for serial communication) or a
\l QModbusTcpServer (for TCP-based communication).
\snippet modbus/server/mainwindow.cpp create_server_0
Once the server is created, the register map is set using
\l QModbusServer::setMap() method. This register map is used by client
applications to read and write server data.
\snippet modbus/server/mainwindow.cpp create_server_1
After that the communication parameters and the server address are
specified. The communication parameters depend on the communication type:
\snippet modbus/server/mainwindow.cpp create_server_2
After the server is created and all the parameters are specified, use
\l QModbusServer::connectDevice() to connect to Modbus network.
\section1 Changing Local Values
The example allows to change values of all supported
\l {QModbusDataUnit::RegisterType}{register types} by using the provided
combo boxes or line edits. Once the value is updated in the UI, the
\l QModbusServer::setData() method is used to update the actual value on
the server:
\snippet modbus/server/mainwindow.cpp update_data_locally
\section1 Handling Remote Writes
The Modbus clients are capable of updating \l {QModbusDataUnit::}{Coils}
and \l {QModbusDataUnit::}{HoldingRegisters} by sending write requests.
Once the value is updated on the server side using such request, a
\l QModbusServer::dataWritten() signal is emitted.
\snippet modbus/server/mainwindow.cpp connect_data_written
The Modbus server example connects to this signal, extracts the updated
values and updates the UI accordingly:
\snippet modbus/server/mainwindow.cpp update_data_from_remote
\include examples-run.qdocinc
*/